Nearly half of the 33.4 million people living with HIV/AIDS worldwide are women. In sub-Saharan Africa, women account for 59 per cent of all infected adults. Young women are especially vulnerable. Worldwide, 60 per cent of the 15 to 24 yr olds with HIV are women and between 70 and 90 per cent of all HIV infections among women are due to heterosexual intercourse. In sub-Saharan Africa, women aged 15 to 24 yr with HIV represent 76 per cent of the total cases in that age group, outnumbering their male peers by three to one. In 2008, an estimated 4.7 million (3.8-5.5 million) people in Asia were living with HIV. India contributes approximately half of Asia’s HIV prevalence and in 2007 an estimated 39 per cent of all HIV infections in India were among women. In addition to biological factors that make women more vulnerable than men to acquiring HIV during sex, various sexual coupling patterns place young women at high risk, including partnering with older men who are more likely to be infected, multiple concurrent relationships, low marriage rates, low consistent condom use rates, and limited skills in negotiating safer sex practices. Gender-based violence increases vulnerability, and poverty increases reliance on transactional sex for survival. Women are often unable to convince their male partners, especially husbands and regular partners, to use condoms. Despite the greater vulnerability of women, they have very few options to reduce the transmission and acquisition of HIV. New technologies to prevent the sexual transmission of HIV in women are urgently needed.